There has been considerable interest in reducing the weight of vehicles and articles used in transportation. This has resulted in a continued search for new lightweight materials, such as composite materials including a metallic layer and a polymeric polymeric layer. Desirably, such materials may offer one or more benefits such as reduced weight, increased stiffness to weight ratio, reduced cost, and the like.
For many applications, it is also desirable for such composite materials to be weldable (i.e., capable of being welded using electrical resistance welding). It has been generally recognized that sandwich composite materials including an insulating polymeric layer are difficult to weld, making them unsuitable for such applications. Attempts to improve the weldability of the composite material have included the addition of conductive fillers in a powder form to the polymeric layer so that the electrical conductivity of the polymeric layer is increased. To compensate for the poor conductivity of the polymer, relatively high levels of conductive powders have been thought necessary. Composite materials including a conductive powder unfortunately have generally poor mechanical properties and generally poor drawability.
Additionally, such material generally requires special equipment for processing (e.g., fabricating, welding, stamping, drawing, and the like). Additionally, it is desirable for a material to have improved weldability, such as may be characterized by a generally high weld current range, by the capability of being welded to a broad range of substrates (preferably using some or all of the same weld parameters), or both.
There continues to be a need for a material that overcomes one or more, or even all of the above. For example, there continues to be a need for a composite material having light weight, increased stiffness to weight ratio, reduced cost, improved weldability, good mechanical properties, good drawability, capable of being processed using existing infrastructure; or any combination thereof.
For welding certain structures, such as thicker section composite materials, articles requiring closely spaced welds, and the like, there may be additional difficulties with welding the composite material. As such, there also has continued to be a need for new welding processes for welding thicker section composite material.